fix(screener): silence ESLint no-empty / no-undef in canvas helpers

빈 catch 블록 3곳에 의도 주석 추가, test-setup.js 의 beforeEach
명시적 import. 우리 신규 코드의 lint error 0으로 정리.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/pages/stock/screener/hooks/useScreenerMode.js

@@ -18,7 +18,7 @@ export function useScreenerMode() {
   const setMode = (m) => {
     if (!VALID_MODES.has(m)) return;
     setModeState(m);
-    try { localStorage.setItem(STORAGE_KEY, m); } catch {}
+    try { localStorage.setItem(STORAGE_KEY, m); } catch { /* ignore quota/security errors */ }
   };
 
   return { mode, setMode };